{"id":547,"date":"2023-01-10T23:51:58","date_gmt":"2023-01-10T23:51:58","guid":{"rendered":"https:\/\/graywolfslair.com\/?p=547"},"modified":"2023-05-15T22:37:34","modified_gmt":"2023-05-15T22:37:34","slug":"15-14-diy-vacuum-chamber","status":"publish","type":"post","link":"https:\/\/graywolfslair.com\/index.php\/15-diy-equipment\/15-14-diy-vacuum-chamber\/","title":{"rendered":"15.14 DIY Vacuum chamber"},"content":{"rendered":"\n

Not only does a vacuum chamber or vacuum oven speed things up, but there are some things that you need one to accomplish.  For those brothers and sisters whom are not bucks up enough to afford to buy one, consider building your own.<\/p>\n\n\n\n

Lots of ways to skin a Duck Billed Platypus, and the simplest vacuum chamber that we’ve found, is a simple pint or quart Bell jar with a bulkhead fitting through the lid.  Don’t try this with the larger jars, as they may implode.<\/p>\n\n\n\n

In this case we are using vacuum to cold boil away the alcohol and the jar would be sitting in warm water.<\/p>\n\n\n\n

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Surplus US military MASH vacuum pump<\/strong><\/p>\n\n\n\n

We’ve also made vacuum chambers out of sanitary spools, as well as Terpenator tanks.  Here is the prototype for a simple lid that we developed for a Terpenator tank.  It is held in place by the vacuum.<\/p>\n\n\n\n

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Plexiglas lids<\/strong><\/p>\n\n\n\n


The prototype shown is a 6″, but with 1 1\/2″ Acrylic or Polycarbonate, you can go up to 12″.<\/p>\n\n\n\n

We also purchased a Pyrex vacuum bell from American Scientific and added a hot plate inside, which allowed us to process up to 6″  Petri dishes.  As we were using a rotary vane AC pump for vacuum, we had to frequently change the oil, as the alcohol condenses in the gear case.<\/p>\n\n\n\n

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Prototype vacuum chamber with hotplate<\/strong><\/p>\n\n\n\n

We also did cold boiling with it, but used a military surplus MASH pump, which doesn’t have a crankcase to flood.  It also only pulls to around 25″ Hg, so it was a slow process.<\/p>\n\n\n\n

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Cold boiling with MASH pump<\/strong><\/p>\n\n\n\n

We tried heated paint pots, which worked, but has a rounded bottom and you can’t see what is going on inside with the solid lid:<\/p>\n\n\n\n

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Pressure paint pot with cable heat and insulation<\/strong><\/p>\n\n\n\n


Next we decided to build one based on a used 22 quart Mirror pressure cooker donated to the cause.  We tossed the lid, but saved the gasket.  I scored some reminant 1 1\/2″ polycarbonate from XXXX Plastics, left over from a bank teller cage job for the lid.<\/p>\n\n\n\n

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Prototype chamber with 2\u201d polycarbonate lid<\/strong><\/p>\n\n\n\n

That brings us to the subject of lid deflection and cracking from high cyclic fatigue.  14.7 psi atmospheric pressure pressing down on a lid is not much, but when you multiply it by the area of the lid, you can see that it mounts up quickly as size increases.<\/p>\n\n\n\n

The real issue is not the deflection, but its effect after repeated cycles from high cyclic fatigue, which manifests itself in multiple fine cracks in the lid, followed as it progresses by a lid failure by implosion.<\/p>\n\n\n\n

Makes a mess, and except for any prestige involved, I encourage you not to do it\u2026…………<\/p>\n\n\n\n

Use a straight edge to check for deflection, and if you are starting from scratch, you can determine the deflection ahead of time.<\/p>\n\n\n\n

Search for formulas from the Thirteenth addition of the Machinery Handbook for calculating stress at the extreme fiber and total deflection for a round plate simply supported, we find the following:<\/p>\n\n\n\n